1. Field of the Invention
The present invention relates to a user data transmission method, in which a mobile station transmits uplink user data using an Enhanced Dedicated Physical Data Channel, and a radio network controller.
2. Description of the Related Art
In a conventional mobile communication system, when setting a Dedicated Physical Channel (DPCH) between a mobile station UE and a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of uplink user data, in consideration of hardware resources for receiving of the radio base station Node B (hereinafter, hardware resource), a radio resource in an uplink (an interference volume in an uplink), a transmission power of the mobile station UE, a transmission processing performance of the mobile station UE, a transmission rate required for an upper application, or the like, and to notify the determined transmission rate of the uplink user data by a message of a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 1, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of uplink user data (for example, per approximately 1 through 100 ms), due to the increase of processing load and processing delay in the radio network controller RNC.
In addition, in the conventional mobile communication system, there has been also a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the uplink user data can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the uplink user data is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 2A, the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 2B, or, as shown in FIG. 2C, by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIGS. 2B and 2C.
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station uE, so as to utilize the uplink radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
Referring to FIG. 3, functions of soft-handover (hereinafter, SHO) in the “Enhanced Uplink” will be described.
In FIG. 3, an example that the mobile station UE which is establishing a radio link with only a cell #10 controlled by the radio base station Node B #1 (hereinafter, the cell which is controlled by the radio base station Node B is indicated as cell), i.e., the mobile station UE in the Non-SHO state shifts to the SHO state in which the mobile station UE is establishing radio links with the cell #10 as well as a cell #20 is shown.
In such a case, the radio base station Node B #1 which controls the cell #10 is configured to perform an error detection check (“Cyclic Redundancy Check (CRC)”) to the uplink user data transmitted from the mobile station UE, and to use a transmission acknowledgement channel (E-HICH: “E-DCH HARQ Acknowledgement Indicator Channel”), so as to reply an ACK or a NACK.
Here, the radio link includes a “Dedicated Physical Channel (DPCH)” or an “Enhanced Dedicated Physical Channel (E-DPCH)” which are established between the mobile station UE and the cell. Accordingly, the SHO state means a state where the mobile station UE is establishing radio links with plurality of cells.
The mobile station UE which has received the ACK is configured to transmit the subsequent uplink user data, and the mobile station UE which has received the NACK is configured to retransmit the transmitted uplink user data.
As described, the radio base station Node B is configured to perform retransmission control according to Hybrid ARQ (HARQ), using the E-HICH.
In step S2001, the mobile station UE is establishing a connection of data (B-DPDCH) for transmitting the uplink user data with the radio network controller RNC via the cell #10.
In step S2002, when the reception power of a common pilot channel from the cell #20 become more than or equal to the predetermined value, the mobile station UE transmits a measurement report to the radio network controller RNC.
In step S2003, the radio network controller RNC requests the cell #20 to establish a synchronization of radio links for uplink between the mobile station UE and the cell #20, based on the transmitted measurement report.
To be more specific, in step S2003, the radio network controller RNC transmits, to the radio base station Node B #2, a SHO setting request including SHO parameters. For example, the SHO parameters include a channelization code for identifying a channel configuration in the radio link for uplink, a scrambling code for identifying the mobile station UE, and a start time of the SHO.
In step S2004, the cell #20 transmits a SHO setting response for indicating that the cell #20 has received the SHO setting request.
In step S2005, the radio network controller RNC requests the mobile station UE to establish a synchronization of radio links for downlink between the cell #20 and the mobile station UE.
To be more specific, in step S2005, the radio network controller RNC transmits, to the mobile station UE, a SHO setting request including the SHO parameters.
In step S2006, the mobile station UE transmits a SHO setting response for indicating that the mobile station UE has received the SHO setting request.
The mobile station UE shifts from the Non-SHO state to the SHO state based on the SHO parameters. In step S2007, the mobile station becomes in the SHO state with the cell #10 and the cell #20.
Here, a set of radio links which are established between the mobile station UE and the radio base station Node B will be called as an “active set”.
The active set will be updated, when the combination of the mobile station UE and the radio base station Node B which establishes the radio link is changed.
For example, the active set will be updated, when the mobile station UE shifts from the Non-SHO state to the SHO state.
Meanwhile, the mobile station UE is configured to perform the retransmission control according to HARQ, using the ACK (or the NACK) received from the radio base station Node B through the E-HICH.
However, in the above mobile communication system, even when the active set is updated based on the shift of the mobile station UE from the Non-SHO state to the SHO state or the like, the information for decoding the E-HICH to be used in the newly connected radio base station Node B (cell) is not notified to the mobile station UE immediately.
Accordingly, after the active set is updated, the mobile station UE cannot decode the ACK (or the NACK) transmitted from the newly connected radio base station Node B, until the information for decoding the E-HICH to be used in the newly connected radio base station Node B is notified to the mobile station UE.
In other words, the mobile station UR cannot determine whether or not to retransmit the transmitted uplink user data to the newly connected radio base station Node B, until the information for decoding the E-HICH is notified to the mobile station UE (that is, the mobile station UE cannot perform the retransmission control according to HARQ).
Accordingly, there has been a problem that the E-DPCH, which is established for transmitting uplink user data fast between the newly connected radio base station Node B and the mobile station UE, is not used efficiently, until the information for decoding the E-HICH to be used in the newly connected radio base station Node B is notified to the mobile station UE after the active set is updated.